The FBI secretly launched an investigation into whether Donald Trump was working on behalf of Russia while in office, according to an explosive report by The New York Times.
The decision was said to have been taken after Mr Trump fired James Comey, the FBI director leading the Russia election meddling investigation at the time, in May 2017.
FBI agents had been weighing up the move for months but decided to act when Mr Trump linked the firing to the relief it would bring from the Russia probe, according to the paper.
The move would have put the FBI in an extraordinary position - having to consider whether the US president himself posed a national security risk to the country he was leading.
The investigation reportedly was only a few days old when Robert Mueller was appointed special counsel to take over the Russia investigation. It is unknown whether he is still pursuing that line of inquiry.
Mr Trump on Saturday morning sent six tweets hitting out at the Russia probe. Referencing the New York Times article, the US president said FBI leaders had launched the investigation “for no reason and with no proof”.
Wow, just learned in the Failing New York Times that the corrupt former leaders of the FBI, almost all fired or forced to leave the agency for some very bad reasons, opened up an investigation on me, for no reason & with no proof, after I fired Lyin’ James Comey, a total sleaze!— Donald J. Trump (@realDonaldTrump) January 12, 2019
The reported decisions date back to the chaotic days in Washington DC after Mr Trump fired Mr Comey just four months into his presidency.
The investigation into Russian election meddling - which included whether Trump campaign figures had conspired with the Kremlin - was already up and running, being led by the FBI.
Mr Trump reportedly wanted to reference Mr Comey’s handling of the Russia investigation in the letter announcing his dismissal. The US president also made the connection in a TV interview, saying “this Russia thing” was a reason he acted.
Those two events convinced FBI leaders that they had to investigate whether Mr Trump was knowingly working for or unwittingly being influenced by Moscow, according to The New York Times.
As well as investigating whether Mr Trump has committed obstruction of justice in firing Mr Comey - a criminal offence - the bureau looked into whether he was a national security threat, which is a counterintelligence matter, the paper reported.
Mr Mueller’s appointed as special counsel around a week after Mr Comey’s firing meant that the FBI handed all aspects of its investigation over to his team.
Rudolph Giuliani, a lawyer for Mr Trump, played down the significance of the investigation to The New York Times, saying: “The fact that it goes back a year and a half and nothing came of it that showed a breach of national security means they found nothing.”
Mr Comey wrote later on Saturday morning:
“I ask you to judge me by the enemies I have made.” — FDR— James Comey (@Comey) January 12, 2019